From e1d92f81e9468f84b4c0a1d1e91a1da50554418f Mon Sep 17 00:00:00 2001
From: ehofman <ehofman>
Date: Fri, 11 Nov 2005 14:46:15 +0000
Subject: [PATCH] Deprecate some non GPL compatible code in favor of our own
 routines.

---
 src/Time/Makefile.am   |   1 -
 src/Time/light.cxx     |   2 +-
 src/Time/sunpos.cxx    | 364 -----------------------------------------
 src/Time/sunpos.hxx    |  33 ----
 src/Time/sunsolver.cxx |  52 +++++-
 src/Time/sunsolver.hxx |   7 +
 src/Time/tmp.cxx       | 127 +++++++++++++-
 src/Time/tmp.hxx       |   2 +
 8 files changed, 186 insertions(+), 402 deletions(-)
 delete mode 100644 src/Time/sunpos.cxx
 delete mode 100644 src/Time/sunpos.hxx

diff --git a/src/Time/Makefile.am b/src/Time/Makefile.am
index 30c9a8b39..98f634176 100644
--- a/src/Time/Makefile.am
+++ b/src/Time/Makefile.am
@@ -3,7 +3,6 @@ noinst_LIBRARIES = libTime.a
 libTime_a_SOURCES = \
 	fg_timer.cxx fg_timer.hxx \
 	light.cxx light.hxx \
-	sunpos.cxx sunpos.hxx \
 	sunsolver.cxx sunsolver.hxx \
 	tmp.cxx tmp.hxx
 
diff --git a/src/Time/light.cxx b/src/Time/light.cxx
index 5eb4f2c17..46e607b16 100644
--- a/src/Time/light.cxx
+++ b/src/Time/light.cxx
@@ -59,7 +59,7 @@
 #include <Main/viewer.hxx>
 
 #include "light.hxx"
-#include "sunpos.hxx"
+#include "tmp.hxx"
 
 
 // Constructor
diff --git a/src/Time/sunpos.cxx b/src/Time/sunpos.cxx
deleted file mode 100644
index f9b87accb..000000000
--- a/src/Time/sunpos.cxx
+++ /dev/null
@@ -1,364 +0,0 @@
-// sunpos.cxx (adapted from XEarth)
-// kirk johnson
-// july 1993
-//
-// code for calculating the position on the earth's surface for which
-// the sun is directly overhead (adapted from _practical astronomy
-// with your calculator, third edition_, peter duffett-smith,
-// cambridge university press, 1988.)
-//
-// Copyright (C) 1989, 1990, 1993, 1994, 1995 Kirk Lauritz Johnson
-//
-// Parts of the source code (as marked) are:
-//   Copyright (C) 1989, 1990, 1991 by Jim Frost
-//   Copyright (C) 1992 by Jamie Zawinski <jwz@lucid.com>
-//
-// Permission to use, copy, modify and freely distribute xearth for
-// non-commercial and not-for-profit purposes is hereby granted
-// without fee, provided that both the above copyright notice and this
-// permission notice appear in all copies and in supporting
-// documentation.
-//
-// The author makes no representations about the suitability of this
-// software for any purpose. It is provided "as is" without express or
-// implied warranty.
-//
-// THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
-// INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
-// IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT
-// OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
-// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
-// NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
-// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
-//
-// $Id$
-
-
-#ifdef HAVE_CONFIG_H
-#  include <config.h>
-#endif
-
-#include <simgear/compiler.h>
-
-#ifdef SG_HAVE_STD_INCLUDES
-#  include <cmath>
-#  include <cstdio>
-#  include <ctime>
-#  ifdef macintosh
-     SG_USING_STD(time_t);
-#  endif
-#else
-#  include <math.h>
-#  include <stdio.h>
-#  include <time.h>
-#endif
-
-#include <simgear/constants.h>
-#include <simgear/debug/logstream.hxx>
-#include <simgear/ephemeris/ephemeris.hxx>
-#include <simgear/math/point3d.hxx>
-#include <simgear/math/polar3d.hxx>
-#include <simgear/math/sg_geodesy.hxx>
-#include <simgear/math/vector.hxx>
-#include <simgear/timing/sg_time.hxx>
-
-#include <Main/globals.hxx>
-#include <Main/viewer.hxx>
-#include <Scenery/scenery.hxx>
-#include <Time/light.hxx>
-
-#include "sunpos.hxx"
-
-// #undef E // should no longer be needed
-#define MeanObliquity (23.440592*(SGD_2PI/360))
-
-static void   ecliptic_to_equatorial(double, double, double *, double *);
-static double julian_date(int, int, int);
-static double GST(time_t);
-
-static void ecliptic_to_equatorial(double lambda, double beta, 
-				   double *alpha, double *delta) {
-    /* double  lambda;            ecliptic longitude       */
-    /* double  beta;              ecliptic latitude        */
-    /* double *alpha;             (return) right ascension */
-    /* double *delta;             (return) declination     */
-
-    double sin_e, cos_e;
-    double sin_l, cos_l;
-
-    sin_e = sin(MeanObliquity);
-    cos_e = cos(MeanObliquity);
-    sin_l = sin(lambda);
-    cos_l = cos(lambda);
-
-    *alpha = atan2(sin_l*cos_e - tan(beta)*sin_e, cos_l);
-    *delta = asin(sin(beta)*cos_e + cos(beta)*sin_e*sin_l);
-}
-
-
-/* computing julian dates (assuming gregorian calendar, thus this is
- * only valid for dates of 1582 oct 15 or later) (after duffett-smith,
- * section 4) */
-
-static double julian_date(int y, int m, int d) {
-    /* int y;                    year (e.g. 19xx)          */
-    /* int m;                    month (jan=1, feb=2, ...) */
-    /* int d;                    day of month              */
-
-    int    A, B, C, D;
-    double JD;
-
-    /* lazy test to ensure gregorian calendar */
-    if (y < 1583) {
-	SG_LOG( SG_EVENT, SG_ALERT, 
-		"WHOOPS! Julian dates only valid for 1582 oct 15 or later" );
-    }
-
-    if ((m == 1) || (m == 2)) {
-	y -= 1;
-	m += 12;
-    }
-
-    A = y / 100;
-    B = 2 - A + (A / 4);
-    C = (int)(365.25 * y);
-    D = (int)(30.6001 * (m + 1));
-
-    JD = B + C + D + d + 1720994.5;
-
-    return JD;
-}
-
-
-/* compute greenwich mean sidereal time (GST) corresponding to a given
- * number of seconds since the unix epoch (after duffett-smith,
- * section 12) */
-static double GST(time_t ssue) {
-    /* time_t ssue;           seconds since unix epoch */
-
-    double     JD;
-    double     T, T0;
-    double     UT;
-    struct tm *tm;
-
-    tm = gmtime(&ssue);
-
-    JD = julian_date(tm->tm_year+1900, tm->tm_mon+1, tm->tm_mday);
-    T  = (JD - 2451545) / 36525;
-
-    T0 = ((T + 2.5862e-5) * T + 2400.051336) * T + 6.697374558;
-
-    T0 = fmod(T0, 24.0);
-    if (T0 < 0) T0 += 24;
-
-    UT = tm->tm_hour + (tm->tm_min + tm->tm_sec / 60.0) / 60.0;
-
-    T0 += UT * 1.002737909;
-    T0 = fmod(T0, 24.0);
-    if (T0 < 0) T0 += 24;
-
-    return T0;
-}
-
-
-/* given a particular time (expressed in seconds since the unix
- * epoch), compute position on the earth (lat, lon) such that sun is
- * directly overhead.  (lat, lon are reported in radians */
-
-void fgSunPosition(time_t ssue, double *lon, double *lat) {
-    /* time_t  ssue;           seconds since unix epoch */
-    /* double *lat;            (return) latitude        */
-    /* double *lon;            (return) longitude       */
-
-    /* double lambda; */
-    double alpha, delta;
-    double tmp;
-
-    /* lambda = sun_ecliptic_longitude(ssue); */
-    /* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
-    //ecliptic_to_equatorial (solarPosition.lonSun, 0.0, &alpha, &delta);
-    
-    /* ********************************************************************** 
-     * NOTE: in the next function, each time the sun's position is updated, the
-     * the sun's longitude is returned from solarSystem->sun. Note that the 
-     * sun's position is updated at a much higher frequency than the rate at 
-     * which the solar system's rebuilds occur. This is not a problem, however,
-     * because the fgSunPosition we're talking about here concerns the changing
-     * position of the sun due to the daily rotation of the earth.
-     * The ecliptic longitude, however, represents the position of the sun with
-     * respect to the stars, and completes just one cycle over the course of a 
-     * year. Its therefore pretty safe to update the sun's longitude only once
-     * every ten minutes. (Comment added by Durk Talsma).
-     ************************************************************************/
-
-    ecliptic_to_equatorial( globals->get_ephem()->get_sun()->getLon(),
-			    0.0, &alpha, &delta );
-    tmp = alpha - (SGD_2PI/24)*GST(ssue);
-    if (tmp < -SGD_PI) {
-	do tmp += SGD_2PI;
-	while (tmp < -SGD_PI);
-    } else if (tmp > SGD_PI) {
-	do tmp -= SGD_2PI;
-	while (tmp < -SGD_PI);
-    }
-
-    *lon = tmp;
-    *lat = delta;
-}
-
-
-/* given a particular time expressed in side real time at prime
- * meridian (GST), compute position on the earth (lat, lon) such that
- * sun is directly overhead.  (lat, lon are reported in radians */
-
-void fgSunPositionGST(double gst, double *lon, double *lat) {
-    /* time_t  ssue;           seconds since unix epoch */
-    /* double *lat;            (return) latitude        */
-    /* double *lon;            (return) longitude       */
-
-    /* double lambda; */
-    double alpha, delta;
-    double tmp;
-
-    /* lambda = sun_ecliptic_longitude(ssue); */
-    /* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
-    //ecliptic_to_equatorial (solarPosition.lonSun, 0.0, &alpha, &delta);
-    ecliptic_to_equatorial( globals->get_ephem()->get_sun()->getLon(),
-			    globals->get_ephem()->get_sun()->getLat(),
-			    &alpha, &delta );
-
-    // tmp = alpha - (SGD_2PI/24)*GST(ssue);
-    tmp = alpha - (SGD_2PI/24)*gst;	
-    if (tmp < -SGD_PI) {
-	do tmp += SGD_2PI;
-	while (tmp < -SGD_PI);
-    } else if (tmp > SGD_PI) {
-	do tmp -= SGD_2PI;
-	while (tmp < -SGD_PI);
-    }
-
-    *lon = tmp;
-    *lat = delta;
-}
-
-
-// update the cur_time_params structure with the current sun position
-void fgUpdateSunPos( void ) {
-    sgVec3 nup, nsun;
-    Point3D rel_sunpos;
-    double dot, east_dot;
-    double sun_gd_lat, sl_radius;
-
-    // vector in cartesian coordinates from current position to the
-    // postion on the earth's surface the sun is directly over
-    sgVec3 to_sun;
-
-    // surface direction to go to head towards sun
-    sgVec3 surface_to_sun;
-
-    FGLight *l = (FGLight *)(globals->get_subsystem("lighting"));
-    SGTime *t = globals->get_time_params();
-    FGViewer *v = globals->get_current_view();
-
-    SG_LOG( SG_EVENT, SG_DEBUG, "  Updating Sun position" );
-    SG_LOG( SG_EVENT, SG_DEBUG, "  Gst = " << t->getGst() );
-
-    double sun_l;
-    fgSunPositionGST(t->getGst(), &sun_l, &sun_gd_lat);
-    l->set_sun_lon(sun_l);
-
-    sgGeodToGeoc(sun_gd_lat, 0.0, &sl_radius, &sun_l);
-    l->set_sun_gc_lat(sun_l);
-
-    Point3D p = Point3D( l->get_sun_lon(), l->get_sun_gc_lat(), sl_radius );
-    l->set_sunpos( sgPolarToCart3d(p) );
-
-    SG_LOG( SG_EVENT, SG_DEBUG, "    t->cur_time = " << t->get_cur_time() );
-    SG_LOG( SG_EVENT, SG_DEBUG,
-	    "    Sun Geodetic lat = " << sun_gd_lat
-	    << " Geocentric lat = " << l->get_sun_gc_lat() );
-
-    // update the sun light vector
-    sgSetVec4( l->sun_vec(), l->get_sunpos().x(),
-	       l->get_sunpos().y(), l->get_sunpos().z(), 0.0 );
-    sgNormalizeVec4( l->sun_vec() );
-    sgCopyVec4( l->sun_vec_inv(), l->sun_vec() );
-    sgNegateVec4( l->sun_vec_inv() );
-
-    // make sure these are directional light sources only
-    l->sun_vec()[3] = l->sun_vec_inv()[3] = 0.0;
-    // cout << "  l->sun_vec = " << l->sun_vec[0] << "," << l->sun_vec[1]
-    //      << ","<< l->sun_vec[2] << endl;
-
-    // calculate the sun's relative angle to local up
-    sgCopyVec3( nup, v->get_world_up() );
-    sgSetVec3( nsun, l->get_sunpos().x(),
-               l->get_sunpos().y(), l->get_sunpos().z() );
-    sgNormalizeVec3(nup);
-    sgNormalizeVec3(nsun);
-    // cout << "nup = " << nup[0] << "," << nup[1] << "," 
-    //      << nup[2] << endl;
-    // cout << "nsun = " << nsun[0] << "," << nsun[1] << "," 
-    //      << nsun[2] << endl;
-
-    l->set_sun_angle( acos( sgScalarProductVec3 ( nup, nsun ) ) );
-    SG_LOG( SG_EVENT, SG_DEBUG, "sun angle relative to current location = "
-	    << l->get_sun_angle() );
-    
-    // calculate vector to sun's position on the earth's surface
-    Point3D vp( v->get_view_pos()[0],
-		v->get_view_pos()[1],
-		v->get_view_pos()[2] );
-    rel_sunpos = l->get_sunpos() - (vp + globals->get_scenery()->get_center());
-    sgSetVec3( to_sun, rel_sunpos.x(), rel_sunpos.y(), rel_sunpos.z() );
-    // printf( "Vector to sun = %.2f %.2f %.2f\n",
-    //         v->to_sun[0], v->to_sun[1], v->to_sun[2]);
-
-    // Given a vector from the view position to the point on the
-    // earth's surface the sun is directly over, map into onto the
-    // local plane representing "horizontal".
-
-    sgmap_vec_onto_cur_surface_plane( v->get_world_up(), v->get_view_pos(),
-				      to_sun, surface_to_sun );
-    sgNormalizeVec3(surface_to_sun);
-    // cout << "(sg) Surface direction to sun is "
-    //   << surface_to_sun[0] << "," 
-    //   << surface_to_sun[1] << ","
-    //   << surface_to_sun[2] << endl;
-    // cout << "Should be close to zero = " 
-    //   << sgScalarProductVec3(nup, surface_to_sun) << endl;
-
-    // calculate the angle between surface_to_sun and
-    // v->get_surface_east().  We do this so we can sort out the
-    // acos() ambiguity.  I wish I could think of a more efficient
-    // way. :-(
-    east_dot = sgScalarProductVec3( surface_to_sun, v->get_surface_east() );
-    // cout << "  East dot product = " << east_dot << endl;
-
-    // calculate the angle between v->surface_to_sun and
-    // v->surface_south.  this is how much we have to rotate the sky
-    // for it to align with the sun
-    dot = sgScalarProductVec3( surface_to_sun, v->get_surface_south() );
-    // cout << "  Dot product = " << dot << endl;
-
-    if (dot > 1.0) {
-        SG_LOG( SG_ASTRO, SG_INFO,
-                "Dot product  = " << dot << " is greater than 1.0" );
-        dot = 1.0;
-    }
-    else if (dot < -1.0) {
-         SG_LOG( SG_ASTRO, SG_INFO,
-                 "Dot product  = " << dot << " is less than -1.0" );
-         dot = -1.0;
-     }
-
-    if ( east_dot >= 0 ) {
-	l->set_sun_rotation( acos(dot) );
-    } else {
-	l->set_sun_rotation( -acos(dot) );
-    }
-    // cout << "  Sky needs to rotate = " << angle << " rads = "
-    //      << angle * SGD_RADIANS_TO_DEGREES << " degrees." << endl;
-}
-
-
diff --git a/src/Time/sunpos.hxx b/src/Time/sunpos.hxx
deleted file mode 100644
index 0fb0df747..000000000
--- a/src/Time/sunpos.hxx
+++ /dev/null
@@ -1,33 +0,0 @@
-/*
- * RCS $Id$
- */
-
-
-#ifndef _SUNPOS_HXX
-#define _SUNPOS_HXX
-
-
-#ifndef __cplusplus                                                          
-# error This library requires C++
-#endif                                   
-
-#include <simgear/compiler.h>
-
-#ifdef SG_HAVE_STD_INCLUDES
-#  include <ctime>
-#else
-#  include <time.h>
-#endif
-
-/* update the cur_time_params structure with the current sun position */
-void fgUpdateSunPos( void );
-
-void fgSunPosition(time_t ssue, double *lon, double *lat);
-
-/* given a particular time expressed in side real time at prime
- * meridian (GST), compute position on the earth (lat, lon) such that
- * sun is directly overhead.  (lat, lon are reported in radians */
-void fgSunPositionGST(double gst, double *lon, double *lat);
-
-
-#endif /* _SUNPOS_HXX */
diff --git a/src/Time/sunsolver.cxx b/src/Time/sunsolver.cxx
index 384761c47..c9bd04efe 100644
--- a/src/Time/sunsolver.cxx
+++ b/src/Time/sunsolver.cxx
@@ -23,15 +23,27 @@
  * $Id$
  */
 
+#ifdef SG_HAVE_STD_INCLUDES
+#  include <cmath>
+// #  include <cstdio>
+#  include <ctime>
+#  ifdef macintosh
+     SG_USING_STD(time_t);
+#  endif
+#else
+#  include <math.h>
+// #  include <stdio.h>
+#  include <time.h>
+#endif
 
 #include <simgear/math/point3d.hxx>
 #include <simgear/math/sg_geodesy.hxx>
+#include <simgear/ephemeris/ephemeris.hxx>
 #include <simgear/timing/sg_time.hxx>
 
 #include <Main/globals.hxx>
 
-#include "sunpos.hxx"
-
+#include "tmp.hxx"
 #include "sunsolver.hxx"
 
 
@@ -39,6 +51,42 @@ static const time_t day_secs = 86400;
 static const time_t half_day_secs = day_secs / 2;
 static const time_t step_secs = 60;
 
+/* given a particular time expressed in side real time at prime
+ * meridian (GST), compute position on the earth (lat, lon) such that
+ * sun is directly overhead.  (lat, lon are reported in radians */
+
+void fgSunPositionGST(double gst, double *lon, double *lat) {
+    /* time_t  ssue;           seconds since unix epoch */
+    /* double *lat;            (return) latitude        */
+    /* double *lon;            (return) longitude       */
+
+    /* double lambda; */
+    double alpha, delta;
+    double tmp;
+
+    double beta = globals->get_ephem()->get_sun()->getLat();
+    double r = globals->get_ephem()->get_sun()->getDistance();
+    double xs = globals->get_ephem()->get_sun()->getxs();
+    double ys = globals->get_ephem()->get_sun()->getys();
+    double ye = globals->get_ephem()->get_sun()->getye();
+    double ze = globals->get_ephem()->get_sun()->getze();
+    alpha = atan2(ys - tan(beta)*ze/ys, xs);
+    delta = asin(sin(beta)*ye/ys + cos(beta)*ze);
+
+    // tmp = alpha - (SGD_2PI/24)*GST(ssue);
+    tmp = alpha - (SGD_2PI/24)*gst;
+    if (tmp < -SGD_PI) {
+        do tmp += SGD_2PI;
+        while (tmp < -SGD_PI);
+    } else if (tmp > SGD_PI) {
+        do tmp -= SGD_2PI;
+        while (tmp < -SGD_PI);
+    }
+
+    *lon = tmp;
+    *lat = delta;
+}
+
 static double sun_angle( const SGTime &t, sgVec3 world_up,
                          double lon_rad, double lat_rad ) {
     sgVec3 nup, nsun;
diff --git a/src/Time/sunsolver.hxx b/src/Time/sunsolver.hxx
index b8be9fe2d..b310fb815 100644
--- a/src/Time/sunsolver.hxx
+++ b/src/Time/sunsolver.hxx
@@ -54,4 +54,11 @@ time_t fgTimeSecondsUntilSunAngle( time_t cur_time,
                                    double target_angle_deg,
                                    bool ascending );
 
+/**
+ * given a particular time expressed in side real time at prime
+ * meridian (GST), compute position on the earth (lat, lon) such that
+ * sun is directly overhead.  (lat, lon are reported in radians
+ */
+void fgSunPositionGST(double gst, double *lon, double *lat);
+
 #endif /* _SUNSOLVER_HXX */
diff --git a/src/Time/tmp.cxx b/src/Time/tmp.cxx
index fec97d074..f734cbd29 100644
--- a/src/Time/tmp.cxx
+++ b/src/Time/tmp.cxx
@@ -25,6 +25,9 @@
 #  include <config.h>
 #endif
 
+#include <simgear/math/vector.hxx>
+#include <simgear/math/polar3d.hxx>
+#include <simgear/math/sg_geodesy.hxx>
 #include <simgear/misc/sg_path.hxx>
 #include <simgear/magvar/magvar.hxx>
 #include <simgear/timing/sg_time.hxx>
@@ -32,9 +35,11 @@
 #include <FDM/flight.hxx>
 #include <Main/fg_props.hxx>
 #include <Main/globals.hxx>
+#include <Main/viewer.hxx>
+#include <Scenery/scenery.hxx>
 
 #include "light.hxx"
-#include "sunpos.hxx"
+#include "sunsolver.hxx"
 #include "tmp.hxx"
 
 
@@ -60,3 +65,123 @@ void fgUpdateLocalTime() {
 					     zone.str() );
 }
 
+
+// update the cur_time_params structure with the current sun position
+void fgUpdateSunPos( void ) {
+    sgVec3 nup, nsun;
+    Point3D rel_sunpos;
+    double dot, east_dot;
+    double sun_gd_lat, sl_radius;
+
+    // vector in cartesian coordinates from current position to the
+    // postion on the earth's surface the sun is directly over
+    sgVec3 to_sun;
+
+    // surface direction to go to head towards sun
+    sgVec3 surface_to_sun;
+
+    FGLight *l = (FGLight *)(globals->get_subsystem("lighting"));
+    SGTime *t = globals->get_time_params();
+    FGViewer *v = globals->get_current_view();
+
+    SG_LOG( SG_EVENT, SG_DEBUG, "  Updating Sun position" );
+    SG_LOG( SG_EVENT, SG_DEBUG, "  Gst = " << t->getGst() );
+
+    double sun_l;
+    fgSunPositionGST(t->getGst(), &sun_l, &sun_gd_lat);
+    l->set_sun_lon(sun_l);
+
+    sgGeodToGeoc(sun_gd_lat, 0.0, &sl_radius, &sun_l);
+    l->set_sun_gc_lat(sun_l);
+
+    Point3D p = Point3D( l->get_sun_lon(), l->get_sun_gc_lat(), sl_radius );
+    l->set_sunpos( sgPolarToCart3d(p) );
+
+    SG_LOG( SG_EVENT, SG_DEBUG, "    t->cur_time = " << t->get_cur_time() );
+    SG_LOG( SG_EVENT, SG_DEBUG,
+	    "    Sun Geodetic lat = " << sun_gd_lat
+	    << " Geocentric lat = " << l->get_sun_gc_lat() );
+
+    // update the sun light vector
+    sgSetVec4( l->sun_vec(), l->get_sunpos().x(),
+	       l->get_sunpos().y(), l->get_sunpos().z(), 0.0 );
+    sgNormalizeVec4( l->sun_vec() );
+    sgCopyVec4( l->sun_vec_inv(), l->sun_vec() );
+    sgNegateVec4( l->sun_vec_inv() );
+
+    // make sure these are directional light sources only
+    l->sun_vec()[3] = l->sun_vec_inv()[3] = 0.0;
+    // cout << "  l->sun_vec = " << l->sun_vec[0] << "," << l->sun_vec[1]
+    //      << ","<< l->sun_vec[2] << endl;
+
+    // calculate the sun's relative angle to local up
+    sgCopyVec3( nup, v->get_world_up() );
+    sgSetVec3( nsun, l->get_sunpos().x(),
+               l->get_sunpos().y(), l->get_sunpos().z() );
+    sgNormalizeVec3(nup);
+    sgNormalizeVec3(nsun);
+    // cout << "nup = " << nup[0] << "," << nup[1] << "," 
+    //      << nup[2] << endl;
+    // cout << "nsun = " << nsun[0] << "," << nsun[1] << "," 
+    //      << nsun[2] << endl;
+
+    l->set_sun_angle( acos( sgScalarProductVec3 ( nup, nsun ) ) );
+    SG_LOG( SG_EVENT, SG_DEBUG, "sun angle relative to current location = "
+	    << l->get_sun_angle() );
+    
+    // calculate vector to sun's position on the earth's surface
+    Point3D vp( v->get_view_pos()[0],
+		v->get_view_pos()[1],
+		v->get_view_pos()[2] );
+    rel_sunpos = l->get_sunpos() - (vp + globals->get_scenery()->get_center());
+    sgSetVec3( to_sun, rel_sunpos.x(), rel_sunpos.y(), rel_sunpos.z() );
+    // printf( "Vector to sun = %.2f %.2f %.2f\n",
+    //         v->to_sun[0], v->to_sun[1], v->to_sun[2]);
+
+    // Given a vector from the view position to the point on the
+    // earth's surface the sun is directly over, map into onto the
+    // local plane representing "horizontal".
+
+    sgmap_vec_onto_cur_surface_plane( v->get_world_up(), v->get_view_pos(),
+				      to_sun, surface_to_sun );
+    sgNormalizeVec3(surface_to_sun);
+    // cout << "(sg) Surface direction to sun is "
+    //   << surface_to_sun[0] << "," 
+    //   << surface_to_sun[1] << ","
+    //   << surface_to_sun[2] << endl;
+    // cout << "Should be close to zero = " 
+    //   << sgScalarProductVec3(nup, surface_to_sun) << endl;
+
+    // calculate the angle between surface_to_sun and
+    // v->get_surface_east().  We do this so we can sort out the
+    // acos() ambiguity.  I wish I could think of a more efficient
+    // way. :-(
+    east_dot = sgScalarProductVec3( surface_to_sun, v->get_surface_east() );
+    // cout << "  East dot product = " << east_dot << endl;
+
+    // calculate the angle between v->surface_to_sun and
+    // v->surface_south.  this is how much we have to rotate the sky
+    // for it to align with the sun
+    dot = sgScalarProductVec3( surface_to_sun, v->get_surface_south() );
+    // cout << "  Dot product = " << dot << endl;
+
+    if (dot > 1.0) {
+        SG_LOG( SG_ASTRO, SG_INFO,
+                "Dot product  = " << dot << " is greater than 1.0" );
+        dot = 1.0;
+    }
+    else if (dot < -1.0) {
+         SG_LOG( SG_ASTRO, SG_INFO,
+                 "Dot product  = " << dot << " is less than -1.0" );
+         dot = -1.0;
+     }
+
+    if ( east_dot >= 0 ) {
+	l->set_sun_rotation( acos(dot) );
+    } else {
+	l->set_sun_rotation( -acos(dot) );
+    }
+    // cout << "  Sky needs to rotate = " << angle << " rads = "
+    //      << angle * SGD_RADIANS_TO_DEGREES << " degrees." << endl;
+}
+
diff --git a/src/Time/tmp.hxx b/src/Time/tmp.hxx
index 64c5c72d4..cc6b0e9cb 100644
--- a/src/Time/tmp.hxx
+++ b/src/Time/tmp.hxx
@@ -38,6 +38,8 @@
 // periodic time updater
 void fgUpdateLocalTime();
 
+// update the cur_time_params structure with the current sun position
+void fgUpdateSunPos( void );
 
 #endif // _LIGHT_HXX
 
-- 
2.39.5